The first enhanced ring planarity based fluorescent “off–on” sensor for Ca2+ ion

The condensation product (L) of benzil and 2-aminophenol acts as fluorescence sensor for Ca2+ ion over metal ions—Na+, K+, Ba2+, Mg2+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, Ag+, Pb2+ and Hg2+, whether present singly or all together along with Cu2+, by “off–on” mode. DFT calculation shows 1:1 interaction between Ca2+ ion and L through the two phenolic O atoms and the dihedral angle between the two phenol rings changes from 40.03° to 9.45°. This Ca2+ ion induced ring planarity is responsible for 5.7 times enhancement in fluorescent intensity of L. Fluorescent and UV/Visible spectroscopic data confirms the 1:1 interaction between L and Ca2+ ion with log β value ca. 4.47.